Finely chop the shrimp and put it in a bowl. Add the ground pork, leeks, and ginger. Stir and lightly mash the ingredients with a fork so that they start coming together. In a separate small bowl, whisk together the sesame oil, cornstarch, soy sauce, salt, and sugar until completely combined. Pour this mixture over the shrimp and pork mixture, and then stir and fold the ingredients together. Once you have broken up any large chunks of pork, briskly stir to blend the ingredients into a cohesive, thick mixture.

Assemble the dumplings: Have a small bowl of cold water ready. Lay a dumpling wrapper on a dry work surface, and place a heaping teaspoon of the meat mixture in the center of the wrapper. With a fingertip moistened with water, trace a line along half of the edge of the round wrapper. Fold the wrapper over to enclose the filling, and press the edges together to seal and form a half-moon shape. Lightly moisten the left end of the half-moon and fold it over the center. Lightly moisten the right end of the half-moon, fold it over the center, and pinch it together with the left end. Push and fold the dumpling to make it stand up. Set aside the stuffed dumpling with the pinched-wrapper edge up. Repeat to make 20 dumplings in all. Keep the finished dumplings at least 1/2 inch apart to prevent them from sticking to each other.

Cook the dumplings: In a large saute pan with a tight fitting lid, heat the vegetable oil over medium-high heat. Carefully place as many of the dumplings that can fit without touching in the skillet with the pinched-wrapper edge up. Cook the dumplings for 3 minutes, or until nicely browned on the bottom. Check the progress by lifting 1 or 2 dumplings by their pinched edge.

Once the bottoms are nicely browned, use the skillet lid to shield yourself from any oil that may splatter, and carefully pour in 1/4 cup of water. Place the lid on the skillet to trap in the moisture and then quickly lower the heat to keep the liquid at a bare simmer.

Check the dumplings after 2 minutes. When the wrappers appear slightly translucent and the meat feels firm when pressed lightly with a spoon, remove the lid and raise the heat slightly. Continue to cook until all the water has evaporated and only the oil remains (about 2 minutes). Once you hear a sizzling sound, shake the skillet. The dumplings should slide about. If they seem to stick to the skillet, move the skillet away from the stove and replace the lid for a moment. Remove the dumplings from the skillet with a broad flexible spatula. If you’d like, flip them over so that the seared surface faces up. Cook any remaining dumplings the same way. Serve the dumplings hot accompanied by the dipping sauce. Garnish with minced chives, if desired.

While the dumplings are cooking, make the dipping sauce by mixing the soy sauce and rice vinegar together in a small bowl. Pour the sauce into a small serving pitcher or distribute among individual dipping dishes.